1. Field of the Invention
The present invention relates to computer networks and to interface devices for connecting host computers to networks. More particularly, the present invention relates to the conservation of power consumption by network interface cards in network connected systems based upon dynamic clock control.
2. Description of Related Art
Computer systems include network interfaces that support high speed data transfer between the host computer and the data network. These network interfaces are typically always on, because of the need to detect traffic on the connected networks, and to detect activity of the host computer which requires service of the network interface card. Thus, in systems for which power conservation is important, the network interface can consume significant power even when it is not downloading packets from the host, transmitting packets on the network, receiving packets from the network or uploading packets to the host.
Network interface cards usually include circuitry that is responsive to a number of different clocks, which are usually asynchronous. For example, a host bus clock, a network receive clock and a network transmit clock are necessary for interfacing with external communication paths. The interface card may also include an internal clock for a variety of logical functions. In order for the network interface to be in a condition to react to activity on its inputs, all of these clocks are left running in the circuitry. Thus, there are many signal transitions consuming power even when the interface card is in an idle state.
Accordingly, it is desirable to provide a network interface card that consumes less power, but remains ready to react efficiently to events on its inputs to transmit and receive data packets, and to react to other commands associated with management of the network interface.
The present invention provides a system and method for connecting constantly running clocks to a small amount of logic on the network interface card. The logic is used to monitor activity on the network interface card, and in response to events enable the clocks for functional blocks within the chip, on an as needed basis. Through dynamically controlled clocks, power consumption can be reduced significantly, and the network interface card remains in a state that is able to react efficiently to external events related to transmission of packets, reception of packets and functions related to the management of the network interface.
Accordingly, the present invention provides a method for managing power consumption on a network interface which manages transfer of data packets between a host processor operating in response to a host clock and a network operating in response to a network clock. The method includes monitoring activity on a first port coupled to the host processor and on a second port coupled to the network, and supplying the host clock and the network clock to circuitry in the network interface on an as needed basis, according to the activity on the first and second ports.
In embodiments in which the network interface includes transmit circuitry responsive to a transmit clock signal and receive circuitry responsive to a receive clock signal, the method includes supplying the transmit clock to circuitry in the transmit path circuitry in response to an event at the first port indicating the transmit sequence, and supplying the receive clock signal to circuitry in the receive path circuitry in response to an event at the second port indicating a receive sequence. The events at the first port indicating a transmit sequence are detected by decoding bus transactions using a decoder that receives a constantly running clock. The events at the second port indicating a receive sequence are detected by filtering packets received from network medium in circuitry which receives a constantly running clock, such as recovering the clock signal from the network.
Some embodiments include an interface between the host processor and a network interface card which comprises a bus operating in response to a bus clock, and the network interface card includes a bus master circuitry and bus slave circuitry. The bus clock is supplied to the bus slave circuitry in response to the detection of an event indicating a bus slave transaction. The bus clock is supplied to the bus master circuitry in response to the detection of an event indicating a bus master transaction.
In another aspect of the invention, for a network interface card including an internal clock, the internal clock is enabled in response to events on the input of the network interface card which can require the resources that rely on the internal clock. In for example, when the transmit circuitry includes a transmit first-in-first-out buffer that receives input data in response to the internal clock and, and supplies output data in response to the transmit clock, the internal clock is enabled in circuitry associated with the first-in-first-out buffer upon detection of events indicating a transmit sequence.
The present invention also provides a computer system which operates more efficiently, and consumes less power, that includes a network interface card with dynamically controlled clocks as described above. In addition, the present invention provides an integrated circuit for use in a network interface card including the logic resources and clock resources associated with dynamically controlled clocks for the functional blocks within the integrated circuit.
Thus, the present invention improves over the state-of-the-art by providing constantly running clocks only in small logic blocks which monitor host processor and network activities. The clocks on bus slave related logic are turned off when there are no bus transactions directed to the network interface. The clocks for the transmit packet buffer and the related download and transmit logic are turned off when there is no packet being downloaded or transmitted. Clocks to the receive packet buffer and the related receive/upload logic are turned off when there is no packet being received or uploaded. The clocks in the medium access controller MAC transmitter are turned off when there is no packet being transmitted to the network. The clocks in the MAC receiver are turned off when there is no packet being received. Overall, power consumption in the network interface card, and in the computer system employing the network interface card are reduced by the use of dynamically controlled clocks among the functional blocks of the network interface card.
Other aspects and advantages of the present invention can be seen upon review of the figures, the detailed description, and the claims which follow.